Various power line communication (PLC) approaches are known in the art. Existing approaches for PLC control are basically carrier frequency based methods that utilize at least one high frequency carrier. For example:
U.S. Pat. No. 4,538,136 (issued to Drabbing) teaches a two frequency keyed signal PLC system having a first predetermined frequency representing a first state of information (e.g., a “0”) and a second predetermined frequency representing a second state of information (e.g. a “1”).
U.S. Pat. No. 6,377,163 (issued to Deller et al) teaches a PLC arrangement having a high frequency communication component that is superimposed on an AC line voltage. A carrier signal that it is transmitted during a time interval coinciding with a positive half cycle of the AC line voltage represents the first state of information, while a carrier signal that is transmitted during a time interval coincident with a negative half cycle of the AC line voltage represents the second state of information. Binary data generated at the PLC transmitter is synchronized with the AC line voltage, assuming a negligible phase shift between the AC line voltages at the transmitter and the receiver.
In the aforementioned patents, the hot and neutral wires of the AC power source are used for transmitting a carrier signal from the transmitter to the receiver.
U.S. Pat. No. 4,016,429 (issued to Vercellotti et al) and U.S. Pat. Nos. 4,408,186 and 4,433,326 (both of which were issued to Howel) teach carrier PLC that is transmitted via the ground and neutral wires of the AC power source. This approach is most suitable for loads in a building that is wired to accommodate grounding connections the loads, which is generally present in building that include electronic ballasts. An advantage of this approach, in comparison with approaches that utilize the hot and neutral wires to transmit a carrier signal, is that the carrier frequency source (transmitter) is not as affected by the 60 Hz high voltage that is provided between the hot and neutral wires.
U.S. Pat. No. 6,842,668 (issued to Carson) disclosed a remotely accessible power controller for building lighting. A major disadvantage of this type of controller is that it requires an isolated interface having an isolated auxiliary power supply (operating directly from the hot and neutral wires of the AC power source), as well as additional band pass filters.
U.S. Pat. No. 5,475,360 (issued to Guidette et al) and U.S. Patent Application 2003/0189495 (filed by Pettler et al) disclose a PLC approach for lighting systems that includes carrier signal receivers (responders) as separate control devices that interface/communicate with one or more ballasts having dimming capabilities.
FIG. 1 describes a common prior art arrangement for providing power line communication (PLC) from an AC power source (not shown in detail) to one or more dimming ballasts for powering gas discharge lamps. As described in FIG. 1, the arrangement includes a responder (i.e., a PLC receiver) that is separate from the dimming ballast(s). During operation, the AC power source generates a carrier control signal, VCONTROL, having an average value of +VIN, as described in FIG. 2. In order to provide binary coding capability, the generation of VCONTROL may be keyed (i.e., timed) to coincide with the positive and negative half cycles of the line voltage, VLINE, provided between the hot and neutral wires of the AC power source. As illustrated in FIG. 3, the carrier control signal is superimposed upon VLINE. Referring back to FIG. 1, the carrier control signal in VLINE is detected and processed by the responder, which then sends an appropriate signal directing the dimming ballast(s) to control the power provided to the lamp(s).
The main drawback of the aforementioned approaches is that the carrier signal receivers and processors are not integrated within the controlled device (e.g., ballasts). For example, in a PLC system for controlling a lamp dimming ballast, the signal receiver is generally referenced to the neutral wire, while the circuitry within the ballast is generally referenced to the negative terminal of bridge rectifier within the ballast. Consequently, additional means are required for providing for signal decoupling, amplifying, and filtering. Accordingly, a relatively expensive and physically large auxiliary AC/DC power supply (that is referenced to the neutral wire of the AC power source) must be provided for the ballast, which makes it very difficult (if not impossible) to mechanical integrate the PLC receiver within the housing of a standard ballast. Consequently, existing PLC systems for lighting applications are generally plagued by high cost and complexity, as well as substantial physical space requirements.
Toward the goal of reducing the size and cost of the PLC receiver, PLC approaches often employ carrier frequencies in excess of 100 kilohertz. Unfortunately, high carrier frequencies are often problematic due to the significant signal attenuation that is caused by the distributed inductances and capacitances that is typically present in the AC wiring of a building. In particular, the distributed inductances and capacitances in the AC wiring places limits upon the maximum permissible physical distance between the control station and the receiver. High frequency carrier approaches have the additional constraint that they must not interfere with operation of AM/FM radios or other PLC systems within the building. These limitations are especially problematic in industrial buildings, where the presence of potentially high levels of noise on the AC power line (i.e., in the voltage between the hot and neutral wires of the AC power source) can seriously compromise the ability to detect and recover high frequency carrier control signals.
Yet another challenge to successfully placing a PLC receiver within a power supply or electronic ballasts is the requirement that the PLC receiver must be compatible with the other circuitry within the power supply or ballast. More particularly, power supplies and electronic ballasts often include active power factor correction (PFC) and inverter circuitry that operates at high frequencies (i.e., in excess of 20 kilohertz) and that, consequently, generates a wide spectrum of noise. A PLC receiver that is mechanically and electrically integrated within a power supply or electronic ballast must be capable of reliably operating is such noisy environments.
Power line communication approaches that utilize a Digital Addressable Lighting Interface (DALI) communication line have become more commonplace in recent years. DALI systems (which are defined in the EN 60929 standard) are intended to provide two-way communication between a power supply/ballast and a control station at the AC power source. A major drawback of DALI approaches is that power supplies and ballasts that utilize DALI require individual supply cables consisting of three power wires (hot, neutral, and ground), as well as two dedicated low voltage signal wires that must be electrically isolated from the main circuitry within the power supply or ballast. The extensive wiring that is required for DALI systems is a major cost impediment to implementing those systems, especially in retrofit applications.
Therefore, a need still exists for reliable PLC methods and circuits that can be readily implemented within existing power supplies and electronic ballasts in a cost-effective and space-efficient manner. Such methods and circuits would represent a significant advance over the prior art.